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Subir Sachdev  One of the best experts on this subject based on the ideXlab platform.

deconfined criticality and ghost Fermi surfaces at the onset of antiferromagnetism in a metal
Physical Review B, 2020CoAuthors: Yahui Zhang, Subir SachdevAbstract:We propose a general theoretical framework, using two layers of ancilla qubits, for a continuous transition between a Fermi liquid with a large Fermi surface, and a pseudogap metal with a small Fermi surface of electronlike quasiparticles. The pseudogap metal can be a magnetically ordered metal, or a fractionalized Fermi liquid (FL*) without magnetic order. A critical 'ghost' Fermi surface emerges (alongside the large electron Fermi surface) at the quantum critical point, with the ghost Fermions carrying neither spin nor charge, but minimally coupled to $(U(1) \times U(1))/Z_2$ or $(SU(2) \times U(1))/Z_2$ gauge fields. Away from the critical point on the pseudogap side, the ghost Fermi surface absorbs part of the large electron Fermi surface, and leads to a jump in the Hall coefficient. We also find an example of an "unnecessary quantum critical point" between a metal with spin density order, and a metal with local moment magnetic order. The ghost Fermions contribute a $T \ln (1/T)$ specific heat at temperature $T$ at the critical point, and could also be detected in other thermal probes. We relate our results to the phases of correlated electron compounds.

antiferromagnetism in metals from the cuprate superconductors to the heavy Fermion materials
Journal of Physics: Condensed Matter, 2012CoAuthors: Subir Sachdev, Max A Metlitski, Matthias PunkAbstract:The critical theory of the onset of antiferromagnetism in metals, with concomitant Fermi surface reconstruction, has recently been shown to be strongly coupled in two spatial dimensions. The onset of unconventional superconductivity near this critical point is reviewed: it involves a subtle interplay between the breakdown of Fermionic quasiparticle excitations on the Fermi surface and the strong pairing glue provided by the antiferromagnetic fluctuations. The net result is a logarithmsquared enhancement of the pairing vertex for generic Fermi surfaces, with a universal dimensionless coefficient independent of the strength of interactions, which is expected to lead to superconductivity at the scale of the Fermi energy. We also discuss the possibility that the antiferromagnetic critical point can be replaced by an intermediate ‘fractionalized Fermi liquid’ phase, in which there is Fermi surface reconstruction but no longrange antiferromagnetic order. We discuss the relevance of this phase to the underdoped cuprates and the heavy Fermion materials.

Fermi surfaces and gaugegravity duality
Physical Review D, 2011CoAuthors: Liza Huijse, Subir SachdevAbstract:We give a unied overview of the zero temperature phases of compressible quantum matter: i.e. phases in which the expectation value of a globally conserved U(1) density,Q, varies smoothly as a function of parameters. Provided the global U(1) and translational symmetries are unbroken, such phases are expected to have Fermi surfaces, and the Luttinger theorem relates the volumes enclosed by these Fermi surfaces tohQi. We survey models of interacting bosons and/or Fermions and/or gauge elds which realize such phases. Some phases have Fermi surfaces with the singularities of Landau’s Fermi liquid theory, while other Fermi surfaces have nonFermi liquid singularities. Compressible phases found in models applicable to condensed matter systems are argued to also be present in models obtained by applying chemical potentials (and other deformations allowed by the residual symmetry at nonzero chemical potential) to the paradigmic supersymmetric gauge theories underlying gaugegravity duality: the ABJM model in spatial dimension d = 2, and the N = 4 SYM theory in d = 3.

weak magnetism and non Fermi liquids near heavy Fermion critical points
Physical Review B, 2004CoAuthors: T Senthil, Matthias Vojta, Subir SachdevAbstract:This paper is concerned with the weakmoment magnetism in heavyFermion materials and its relation to the nonFermi liquid physics observed near the transition to the Fermi liquid. We explore the hypothesis that the primary fluctuations responsible for the nonFermi liquid physics are those associated with the destruction of the large Fermi surface of the Fermi liquid. Magnetism is suggested to be a lowenergy instability of the resulting small Fermi surface state. A concrete realization of this picture is provided by a fractionalized Fermi liquid state which has a small Fermi surface of conduction electrons, but also has other exotic excitations with interactions described by a gauge theory in its deconfined phase. Of particular interest is a threedimensional fractionalized Fermi liquid with a spinon Fermi surface and a U(1) gauge structure. A direct secondorder transition from this state to the conventional Fermi liquid is possible and involves a jump in the electron Fermi surface volume. The critical point displays nonFermi liquid behavior. A magnetic phase may develop from a spin density wave instability of the spinon Fermi surface. This exotic magnetic metal may have a weak ordered moment although the local moments do not participate in the Fermi surface. Experimental signatures of this phase and implications for heavyFermion systems are discussed.
T Senthil  One of the best experts on this subject based on the ideXlab platform.

translationally invariant non Fermi liquid metals with critical Fermi surfaces solvable models
arXiv: Strongly Correlated Electrons, 2018CoAuthors: Debanjan Chowdhury, Yochai Werman, Erez Berg, T SenthilAbstract:We construct examples of translationally invariant solvable models of stronglycorrelated metals, composed of lattices of SachdevYeKitaev dots with identical local interactions. These models display crossovers as a function of temperature into regimes with local quantum criticality and marginalFermi liquid behavior. In the marginal Fermi liquid regime, the dc resistivity increases linearly with temperature over a broad range of temperatures. By generalizing the form of interactions, we also construct examples of nonFermi liquids with critical Fermisurfaces. The self energy has a singular frequency dependence, but lacks momentum dependence, reminiscent of a dynamical mean field theorylike behavior but in dimensions $d<\infty$. In the low temperature and strongcoupling limit, a heavy Fermi liquid is formed. The critical Fermisurface in the nonFermi liquid regime gives rise to quantum oscillations in the magnetization as a function of an external magnetic field in the absence of quasiparticle excitations. We discuss the implications of these results for local quantum criticality and for fundamental bounds on relaxation rates. Drawing on the lessons from these models, we formulate conjectures on coarse grained descriptions of a class of intermediate scale nonFermi liquid behavior in generic correlated metals.

Critical Fermi surfaces and nonFermi liquid metals
Physical Review B, 2008CoAuthors: T SenthilAbstract:At certain quantum critical points in metals an entire Fermi surface may disappear. A crucial question is the nature of the electronic excitations at the critical point. Here we provide arguments showing that at such quantum critical points the Fermi surface remains sharply defined even though the Landau quasiparticle is absent. The presence of such a critical Fermi surface has a number of consequences for the universal phenomena near the quantum critical point which are discussed. In particular the structure of scaling of the universal critical singularities can be significantly modified from more familiar criticality. Scaling hypotheses appropriate to a critical Fermi surface are proposed. Implications for experiments on heavy Fermion critical points are discussed. Various phenomena in the normal state of the cuprates are also examined from this perspective. We suggest that a phase transition that involves a dramatic reconstruction of the Fermi surface might underlie a number of strange observations in the metallic states above the superconducting dome.

weak magnetism and non Fermi liquids near heavy Fermion critical points
Physical Review B, 2004CoAuthors: T Senthil, Matthias Vojta, Subir SachdevAbstract:This paper is concerned with the weakmoment magnetism in heavyFermion materials and its relation to the nonFermi liquid physics observed near the transition to the Fermi liquid. We explore the hypothesis that the primary fluctuations responsible for the nonFermi liquid physics are those associated with the destruction of the large Fermi surface of the Fermi liquid. Magnetism is suggested to be a lowenergy instability of the resulting small Fermi surface state. A concrete realization of this picture is provided by a fractionalized Fermi liquid state which has a small Fermi surface of conduction electrons, but also has other exotic excitations with interactions described by a gauge theory in its deconfined phase. Of particular interest is a threedimensional fractionalized Fermi liquid with a spinon Fermi surface and a U(1) gauge structure. A direct secondorder transition from this state to the conventional Fermi liquid is possible and involves a jump in the electron Fermi surface volume. The critical point displays nonFermi liquid behavior. A magnetic phase may develop from a spin density wave instability of the spinon Fermi surface. This exotic magnetic metal may have a weak ordered moment although the local moments do not participate in the Fermi surface. Experimental signatures of this phase and implications for heavyFermion systems are discussed.
Xiaoli Dong  One of the best experts on this subject based on the ideXlab platform.

Distinct Fermi Surface Topology and Nodeless Superconducting Gap in a ( Tl 0.58 Rb 0.42 ) Fe 1.72 Se 2 Superconductor
Physical Review Letters, 2011CoAuthors: Daixiang Mou, Shanyu Liu, Xiaowen Jia, Yingying Peng, Lin Zhao, Guodong Liu, Xiaoli DongAbstract:High resolution angleresolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the (Tl0.58Rb0.42)Fe1.72Se2 superconductor with a Tc = 32 K. The Fermi surface topology consists of two electronlike Fermi surface sheets around the Gamma point which is distinct from that in all other ironbased superconductors reported so far. The Fermi surface around the M point shows a nearly isotropic superconducting gap of similar to 12 meV. The large Fermi surface near the Gamma point also shows a nearly isotropic superconducting gap of similar to 15 meV, while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in ironbased superconductors.

distinct Fermi surface topology and nodeless superconducting gap in a tl0 58rb0 42 fe1 72se2 superconductor
Physical Review Letters, 2011CoAuthors: Daixiang Mou, Xiaoli Dong, Shanyu Liu, Xiaowen Jia, Yingying Peng, Lin Zhao, Guodong Liu, Jun Zhang, Hangdong Wang, Chiheng DongAbstract:High resolution angleresolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the (Tl0.58Rb0.42)Fe1.72Se2 superconductor with a Tc = 32 K. The Fermi surface topology consists of two electronlike Fermi surface sheets around the Gamma point which is distinct from that in all other ironbased superconductors reported so far. The Fermi surface around the M point shows a nearly isotropic superconducting gap of similar to 12 meV. The large Fermi surface near the Gamma point also shows a nearly isotropic superconducting gap of similar to 15 meV, while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in ironbased superconductors.
Daixiang Mou  One of the best experts on this subject based on the ideXlab platform.

Distinct Fermi Surface Topology and Nodeless Superconducting Gap in a ( Tl 0.58 Rb 0.42 ) Fe 1.72 Se 2 Superconductor
Physical Review Letters, 2011CoAuthors: Daixiang Mou, Shanyu Liu, Xiaowen Jia, Yingying Peng, Lin Zhao, Guodong Liu, Xiaoli DongAbstract:High resolution angleresolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the (Tl0.58Rb0.42)Fe1.72Se2 superconductor with a Tc = 32 K. The Fermi surface topology consists of two electronlike Fermi surface sheets around the Gamma point which is distinct from that in all other ironbased superconductors reported so far. The Fermi surface around the M point shows a nearly isotropic superconducting gap of similar to 12 meV. The large Fermi surface near the Gamma point also shows a nearly isotropic superconducting gap of similar to 15 meV, while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in ironbased superconductors.

distinct Fermi surface topology and nodeless superconducting gap in a tl0 58rb0 42 fe1 72se2 superconductor
Physical Review Letters, 2011CoAuthors: Daixiang Mou, Xiaoli Dong, Shanyu Liu, Xiaowen Jia, Yingying Peng, Lin Zhao, Guodong Liu, Jun Zhang, Hangdong Wang, Chiheng DongAbstract:High resolution angleresolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the (Tl0.58Rb0.42)Fe1.72Se2 superconductor with a Tc = 32 K. The Fermi surface topology consists of two electronlike Fermi surface sheets around the Gamma point which is distinct from that in all other ironbased superconductors reported so far. The Fermi surface around the M point shows a nearly isotropic superconducting gap of similar to 12 meV. The large Fermi surface near the Gamma point also shows a nearly isotropic superconducting gap of similar to 15 meV, while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in ironbased superconductors.
Sabine Andergassen  One of the best experts on this subject based on the ideXlab platform.

Soft Fermi surfaces and breakdown of Fermiliquid behavior.
Physical review letters, 2003CoAuthors: Walter Metzner, Daniel Rohe, Sabine AndergassenAbstract:Electronelectron interactions can induce Fermi surface deformations which break the pointgroup symmetry of the lattice structure of the system. In the vicinity of such a "Pomeranchuk instability" the Fermi surface is easily deformed by anisotropic perturbations, and exhibits enhanced collective fluctuations. We show that critical Fermi surface fluctuations near a dwave Pomeranchuk instability in two dimensions lead to large anisotropic decay rates for singleparticle excitations, which destroy Fermiliquid behavior over the whole surface except at the Brillouin zone diagonal.